Master switch and control system combination



y 1943- B. E. MCARTHUR ET AL 2,325,413

MASTER SWITCH AND CONTROL SYSTEM COMBINATION Filed Sept. 10, 1942 b 2Sheets-Sheet 1 INVENTOR3 BRUCE EMCARTHUR &

ASA HMYLE I v v Mj-W MASTER SWITCH AND CONTROL SYSTEM COMBINATION FiledSept. 10, 1942 2 Sheets-Sheet 2 INVENTORS BRUCE E.McARTHUR 8,

ASA H. MYLES F/GZ BY Patented July 27, 1943 MASTER SWITCH AND CONTROLSYSTEM COMBINATION Bruce E. McArthur, East Cleveland, and Asa H. Myles,Solon, Ohio, assignors to The Electric Controller & ManufacturingCompany, Cleveland, Ohio, a corporation of Ohio Application September10, 1942, Serial No. 457,802

11 Claims.

This invention relates to electric systems of control for alternatingcurrent induction motors which are utilized as driving motors forapparatus in which the load at time overhauls the motor and drives it,and in which the overhauling load must be retarded to prevent theoverhauling speed from becoming excessive. The invention is particularlyapplicable to hoist motors which may be overhauled and driven by adescending load and the invention is hereinafter described as applied tothat use.

Heretofore, when polyphase wound rotor induction motors have been usedto operate electric hoists, descending over-hauling loads have beenretarded by connecting the motor to a source of power havingpreponderantly polyphase characteristics for causing the motor to exerta reduced motor torque which opposes but does not exceed the torque ofthe load. Since the counter-torque, or reduced motor torque whichopposes the torque of the descending load, is obtained by connecting theprimary winding of themotor to the source of power in the same manner asfor hoisting, the counter-torque operation often has been controlledfrom the hoisting positions of the master switch. For example, in acopending application of Harry L. Wilcox, Serial No. 408,153, filedAugust 25, 1941, there is disclosed a control system for a polyphasewound rotor induction motor subject to overhauling loads in whichseveral values of counter-torque and a value of single phase brakingtorque are selectively available, but in which the counter-torque isavailable only when the master switch is in a hoisting position. The

single phase braking action results from the rotation of a rotor circuitof high resistance through an unsymmetrical field set up due toenergization of the primary from a source of power having preponderantlysingle phase characteristics and the presence of a local closed path oflow resistance in the primary circuit. As used herein, single phasesource of power refers to a source having preponderantly single phasecharacteristics and single phase braking refers to braking actionobtained by connecting the primary to such a source with a portion ofthe primary short circuited, i. e. connected in a local circuit of lowimpedance. Since in the control system of the Wilcox application a loadcan be lowered by either single phase braking, power or regenerativelowering, or counter-torque lowering, it is confusing to a craneoperator to have to move the master switch to what is normally ahoisting position'in order to use one of these methods of lowering,whereas the other two methods are available from the usual or naturallowering posi-- master switch is in what is normally the hoistingpositions, only hoisting connections be available.

Prior control systems which provide only counter-torque lowering andpower or regenerative lowering have, been arranged, but in such systemsthe master switch must be moved from a neutral or off" position throughits lowering zone to the end of the lowering zone farthest from theneumaster switch from the remote end of the -lowering zone, the motor isconnected for countertorque operation. Both counter-torque lowering andpower or regenerative lowering thus are obtained from the same side orlowering zone of the master switch, but counter-torque lowering isobtained only after the master switch is returned part way from theremote end of the lowering zone.

However, adding single phase braking to a counter-torque control systemsuch as just described, presents several diiiiculties, for example, theportion or sub-zone of the lowering zone nearest the 011 position is thebest for single phase braking operation because of the excellent inchingcontrol thereby rendered available, but since the positions between thenearest and farthest positions of the lowering zone are ineffectiveuntil after the masterswitch has been moved to the farthest position,uniform operation in response to master switch movement is not possiblebecause the friction brake must be released when the single phasebraking sub-zone is reached and re-applied during the time of movementof the master switch to the farthest position in the lowering zone.

In accordance with this invention a combined single phase braking andcounter-torque lowering controller is provided in which the positionnearest the off position normally is the single I phase braking sub-zoneand all other positions beyond the single phase sub-zone provide poweror regenerative lowering and in which an auxiliary manual means isoperable while the master switch is in any of the lowering positions toalter the control connections so that counter-torque lowering isthereafter available throughout the lowering zone; thus in effectchanging the lower 1 ing zone to a counter-torque zone.

More specifically, when the master switch is in the lowering zone,movement of the auxiliary manual means to one of its two positionscauses disconnection of the motor from the source of power supply andapplication of a magnetically released friction brake which holds theload at a standstill. Movement of the manual means to its secondposition after movement to its first position and while the masterswitch is still in the lowering zone reconnects the motor to the sourceof power so that the motor exerts a countertorque. Operation of themanual means causes unbalancing of the secondary circuit of the motor sothat the hoisting or counter-torque of the motor is reduced below thatobtainable when the master switch is in the hoisting positions.Subsequent movement of the manual means between its first and secondpositions provides additional inching control of the load.

.By means of the present invention single phase braking, power orregenerative lowering, and counter-torque lowering all are renderedavailable while the master switch is in what ordinarily is the loweringzone without increasing the number of lowering positions. Thecountertorque is obtained by unbalancing of the secondary resistor sothat the tendency to hoist loads by counter-torque is limited. As themaster switch is moved away from it neutral position through thelowering zone, the counter-torque diminishes, thereby causing thecounter-torque lowering speeds to increase away from neutral in onedirection in the same manner as the hoisting speed increases as themaster switch is moved away from its neutral position in the otherdirection through the hoisting positions. Furthermore, once the shifthas been made from power lowering to counter-torque connections, themotor connections cannot be changed back to power lowering or singlephase braking until the master switch is returned to the neutralposition.

. It is an object of this invention to provide an improved controlsystem for a wound rotor induction motor subject to overhauling loads.

Another object is to provide a control system for a wound rotorinduction motor used for hoisting service which provides a simple andcentralized control of counter-torque, single phase braking, and poweror regenerative lowering and in which all three are available from thesame group of positions of the usual multi-position master switch at theoption of the operator.

A further object is to provide a control system for a wound rotorinduction motor used for hoisting service in which the operator at willcan select either single phase braking, power or regenerative lowering,or counter-torque lowering operations and in which the counter-torque isnormally less than the available hoisting torque and is obtained whilethe master switch is in what is normally the lowering zone.

A further object is to provide a simple hoist control system which iscapable of connecting a polyphase wound rotor induction motor for powerhoisting when a master switch is on one side of a neutral position andwhich is capable of connecting the motor selectively for power orregenerative lowering, single phase braking, or counter-torque loweringwhen the master switch is on the other side of the neutral position.

Another object is to provide an improved control system for a woundrotor induction motor used for hoist service, and having amulti-posiergization and friction braking and any one of severalcounter-torque values is accomplished by push button manipulation.

A correlative and more specific object is to rovide a control system andmaster switch combination such that, as the master switch is moved intreme positions, it normally starts by providing maximum hoisting speed,gradually decreases the speed to minimum hoisting speed, then in order,passes to "ofi condition, to single phase braking, to minimum and thento maximum power lowering acceleration, and in the reverse directionperforms said operations in reverse order, and in which by the operationof an auxiliary manual means, the single phase braking and powerlowering positions or zones are rendered operative as counter-torqueposition in which the counter-torque decreases as the master switch ismoved from the off position in the direction which normally causes powerlowering acceleration to increase.

Other objects and advantages will become apparent from the followingspecification wherein reference is made to the drawings, in which Figure1 is a complete power circuit and a partial control circuit diagram of acontrol system embodying the invention, and v Figure 2 is a diagram ofthe remainder of the control circuit of Figure 1 and combines therewithto complete the circuit diagram.

Referring to Fig. 1, a wound rotor induction motor I0 has its primarywinding ll arranged to be energized from a source of three phase powerrepresented by the conductors Ll, L2, and L3. A Y-connected motor isillustrated in the drawings, but the control system herein described canbe used with a delta connected motor as well. The primary winding H hasthree terminals 1, 8 and 9. For causing the motor In to exert a torquein a direction to assist in lowering a load the terminal 8 is connectedto the conductor Ll through contacts [511, the terminal 1 is connectedto the conductor L2 through contacts lib and Mia, and the terminal 9 isconnected to the conductor L3 through contacts i6b. For causing themotor I0 to exert a torque in a direction tending to hoist a load theconnections from the terminals 1 and 9 to the conductors L2 and L3 arereversed through contacts Fla and Nb. For single phase brakingoperation, the. terminals 1 and 8 are interconnected through contacts18a and I8b and a point on the interconnection is connected to theconductor L2 through a conductor 39 ard the contacts Ito, and theterminal 9 is conneocd to the conductor L3 through the contacts 5b.

The motor III has a secondary winding l2 connected through slip rings toa polyphase network comprising a Y-connected resistor 20 having each ofits three branches 2|, 22, and 23 divided into five resistance sectionsa, b, c, d, and r which are referred to by using those letters assubscripts to the reference character of the corresponding branch. Thusthe branch 2| comprises the sections 2la, Zlb, 2|c, 2ld, and Mr. Thesections 2", 221', and 231' are arranged to be short circuited bycontacts 25a, 25b, and 25c, respectively. The resistance sections 2| a,22a, and 23a are of equal ohmic value and are arranged to be shortcircuited by contacts 26a. and 26b; the additional resistance sections2lb, 22b and 23b are of equal ohmic value and together with the section2Ir are arranged to be short circuited by contacts 21a and 21b; theadditional resistance sections 2 lo, 220 and 23c are of equal ohmicvalue one direction from one to the other of its exand together with thesection 221' are arranged to be short circuited by contacts 28a and 28b;and the additional resistance sections 2Id, 22d and 23d are of equalohmic value and are arranged to be short circuited by contacts 29a and29b. The resistance sections 2|r, 221-, and "231* preferably are ofequal ohmic value, but may be unequal if desired. Preferably, theresistance of the sections. 2|a, 22a, and 23a is about onehalf of thetotal resistance of the resistor net work 20.

Acceleration of the motor I may be controlled by the relays 3|, 4| andof relay circuits 30, 40 and 50, respectively, which are connectedacross voltage dividers 32, 42 and 52, respectively. The voltagedividers 42 and 52 are connected in parallel across one of the branchesof the secondary resistor 20 shown as the branch 23, one connectionbeing adjustable along the,

section 230. as shown, and the voltage divider 32 is connected across adifferent branch of the secondary resistor 20, shown as branch 2|, oneconnection being adjustable along the section 2 Ia as shown. The relay3| has an operating winding 3|wand normally closed contacts 3|a and 3| band the relay 4| has an operating winding 4|w and normally closedcontacts Ho and M1). The relay 5| has an operating winding 5|w andnormally closed contacts 5Ia.

In the relay circuit 30 the relay operating winding 3| w, a condenser33, and normally open contacts |5c are connected in series across anadjustable portion of the voltage divider 32 to form a series resonantcircuit 30a. Also connected in series with the winding 3Iw across anadjustable portion of the voltage divider 32 and forming with thewinding 3|w a series-parallel resonant circuit 30b are normally opencontacts 260, normally closed contacts I5d, and a parallel circuitincluding a condenser 34 and a non-saturable reactor 35.

In the relay circuit 40 the relay operating winding 4|w, a condenser 43,and normally open contacts 46a are connected in series across anadjustable portion of the voltage divider 42 to form a series resonantcircuit 40a. Also connected in series with the winding 4|w across anadjustable portion of the voltage divider 42 and forming with thewinding 4|w a series-parallel resonant circuit 402) are normally opencontacts 26d, normally closed contacts 46b, and a parallel circuitincluding a condenser 44 and a nonsaturable reactor 45.

In the relay circuit 50 the relay operating winding 5|w and a condenser53 are connected in series across an adjustable portion of the voltagedivider 52 to form a series resonant circuit.

For preventing excessive speeds during counter-torque lowering a seriesresonant relay circuit I20 is provided. The relay circuit I20 isconnected across an adjustable portion of the voltage divider 52, andcomprises a series circuit including a condenser I23 and an operatingwinding |2|w of a relay |2| having normally open contacts I2Ia.

The relay circuits 50 and I20 and the series resonant portions 30a and40a of the relay circuits 30 and 40 are of the type disclosed andclaimed in Patent No. 2,165,491, issued July 11, 1939, to J. D. Leitch,and the series-parallel resonant portions 30b and 40b of the relaycircuits 30 and 40 are of the type disclosed and claimed in Patent No.2,232,257, issued to A. H. Myles on February 18, 1941. As more fullydescribed in these patents, the electrical constants of the ciatedcontacts open.

capacitances and inductances in the relay circuits 30, 40 and 50 are sochosen in relation to each other and to the magnitude and frequency ofthe secondary voltage drop to which the relay circuits 30, 40 and 50 aresubjected that the relay windings 3Iw, M10, and 5Iw are sufficientlyenergized at certain predetermined speeds of the motor ID to maintaintheir rerespective associated contacts open, but are not sufiicientlyenergized at certain other speeds of the motor II) to maintain theirrespective asso- The reactances of the winding |2|w and the condenserI23 are so chosen-that for all safe counter-torque lowering speeds thecontacts |2| a remain open, but are closed as soon as the counter-torquelowering speed reaches an excessive value.

The control circuits of Fig. 2 are energized from the conductors L2 andL3 through the conductors |3 and I4 when a knife switch I9, shown inFig. 1, is closed. A spring applied, electromagnetically releasedfriction brake 41 for the motor I0 has a direct current operatingwinding 41w connected through normally open contacts 48a to the directcurrent terminals of a suitable rectifier 49 having its alternatingcurrent terminals connected across the conductors I3 and I4 throughnormally open contacts 48b.

Operating means for all of the contacts shown in Fig. 1 except those ofthe relays 3|, 4|, 5|, and |2| are shown in Fig. 2. The contacts shownin 'Fig. 1 and referred to by numerals with distinguishing subscripts,except those of the relays 3|, 4|, 5| and |2I, are parts of theelectromagnetic contactors or relays shown completely in Fig. 2. Thecontacts of the various relays and contactors are also shown at theirpositions in the circuit as well as in conjunction with the showing ofthe complete contactor or relay. Each of the complete contactors orrelays is referred to by the same reference numeral as its parts butwithout any subscript. Each of the contactors or relays has an operatingwinding which is referred to by the reference numeral of its associatedcontactor or relay and the subscript w.

Referring now to Fig. 2, a low voltage protection relay 36 has anoperating winding 36w and normally open contacts 36a. A push button 31controls, over a circuit to be described, the energization of a pair ofrelays 38 and 39. The relay 38 has an operating winding 38w, normallyopen contacts 38a, 38b, and 38c, and normally closed contacts 380 and38d; and the relay 39 has an operating winding 39w, normally opencontacts 39a, and normally closed contacts 39b. A transfer relay 49having an operating winding 49w and normally open contacts 49a, 49b, and490 is also provided.

A multi-position master switch having a plurality of circuit terminals6| movable from an off position through five successive loweringpositions in a lowering zone and five successive hoisting position in ahoisting zone is provided for controlling the operation of the variouscontactors and relays which effect operation of the motor I0. The masterswitch 60 has lowering contact segments 62-10 inclusive, hoistingcontact segments 1|-16 inclusive, a contact segment 11 which engages oneof the circuit terminals 6| in all posi tions, and a contact segment 19which engages two of the circuit terminals 6| only in the off position.The contact segments 62-11 inclusive are electrically interconnected.The push button 31 is preferably mounted in the operating handle of themaster switch 60 in a well known manner.

As will become apparent from the following description, the loweringzone of the master-switch 60 comprises a singlephase braking sub-zoneand a power lowering sub-zone contiguous to each other and with thesingle phase braking sub-zone contiguous to the off position. Thehoisting zone is also contiguous to the off position but is on theopposite side thereof from the lowering zone.

A more complete understanding of this invention may be had from aconsideration of its operation. Assuming that the switch I9 is closed,if the master switch 60 is in the ofi position, an energizing circuitfor the operating winding 35w of the relay 36 is completed from theconductor L3 through the switch I9, the conductor I3, a conductor 86,one of the circuit terminals BI, the contact segment I8, another of thecircuit terminals BI, a conductor 81, the winding 36w, the conductor I4,and the knife switch I9 to the conductor L2. As a result of theenergization of its operating winding 36w, the relay 36 operates toclose its contacts 36a which complete a circuit directly between theconductor I3 and the conductor 81 to maintain the. winding 36w energizedregardless of the position of the master switch 60. A conductor 88electrically connects the conductor 81 to the circuit terminal 6| whichis in engagement with the contact segment 11 to maintain a connectionbetween the contact segments 62-", inclusive, and the conductor L3 atall times when the contacts 36a and the switch I9 are closed or when themaster switch is in the off position and the switch I9 is closed.

Concurrently with the energization of the winding 3611), the operatingwinding 25w is energized causing the contactor 25 to close its contacts25a, 25b. and 250 which short circuit the resistance sections 2Ir, 221,and 231', respectively, and to close its contacts 25d and 25a in thecircuits to the operating windings I61 and 26w, respectively. Thewinding 25w is connected in parallel with the winding 36w betweentheconductor 81 and the conductor I4 through the normally closedcontacts 38d. The contacts 38d are closed at all times to maintain thecontactor 25 in its energized position except after operation of thepush for the winding 48w which when energized main- I tains the contacts48a and 48b closed is completed in all lowering positions from thesegment I0 and in all hoisting positions from the segment 16 through aconductor I8, the winding 58w, a

conductor H4, and the normallyclosed contacts 39b to the conductor is.As long as the contacts 39b are closed, the conductor W5 remainsconnected to the conductor L2 of the source throu h.

the conductor I 4 and the switch I 9.

Assuming that a load is to be hoisted by the motor III, the masterswitch Gfi may be moved to the first position in the hoisting zone tothereby complete an energizing circuit for the winding I In; from thecontact segment I2 through aconductor 96, the winding I'Iw, a conductor38, and

the contacts id to the conductor 'IM. In response to the energization ofits operating wind,-

. ing IIw the contactor II closes its contacts I'Ia,

IIb, I10 and Hit. Closure of the contacts IIb connects the terminal 9 orthe primary winding II to the conductor L2, closure of the contacts'I'Ia partially completes a circuit from the terminal I of the windingII to the conductor L3, closure of the contacts IIc completes anenergizing circuit for the winding I5w from the conductor 96 through theconductor 91, the contacts He, the winding I5w, conductors 99 and 98,and the contacts I812 to the conductor I I4. Closure of the contacts lidin a circuit to the winding 26w has no operative effect at this time.

In response to the energization of its operating winding l5w, thecontactor I5 operates to close its contacts I5a, I5b, I50, and I5e andto open its contacts I5d and I5 Closure of the contacts I5a connects theterminal 8 of the primary winding II to the conductor LI, and closure ofthe contacts I5b completes the connection of the terminal I to theconductor L3. Closure of the contacts I5c completes the series resonantrelay circuit 30a. Opening of the contacts l5d insures that theseries-parallel relay circuit 301) is interrupted during hoisting andopening of the contacts I51 interrupts an interlock circuit with thewinding I820. Closure of the contacts I59 completes an energizingcircuit for. the operating winding 4610 of the relay 46 from theconductor 9? through the contacts He, a conductor 89, the coniiairgtsI5e, and the winding 46w to the conductor As a result of theenergization of its operating winding 4621), the relay 46 closes itscontacts 46a to complete the series resonant circuit 40a, opens itscontacts 461) to insure that the seriesparallel resonant circuit 401) isinterrupted during hoisting, and closes its contacts 460 to partiallycomplete an energizing circuit for the operating winding 2-110 of thecontactor 21.

When the master switch 60 is in the first hoisting position, thecontactors I5 and I! are in their energized positions and the motor I0is so connected to the source as to tend to accelerate a load upward.-Allof the sections of the resistor 20 except the r sections areconnected in the secondary circuit so that the torque of the motor I0 iscomparatively low. When the primary winding II is first connected to thesource, the induced current in the secondary winding I2 is of acomparatively high magnitude and frequency so that the voltage dropacross the branches 2| and 323 of the resistor 20. causes energizationof [the windingsSIw, M10, and Sin; of the relays 3i, LII, and 5 6., Therelays 3I, AI, and 5| are therefore in. their energized positions andthe contacts sia, Mb, film-Alb, and Ho are open.

Movement of'the master switch 60 to the sec- 0nd position-infthe'hoisting zone causes energization ioi the winding 26w over a circuitfrom thecontact segment I3 through a conductor 90, the contacts 25c andNe, a, conductor H5, and the winding-25w to the conductor II I. As aresult of the energization of its operating winding fifimthecontactor 26closes its contacts 26a and 26b to short circuit the resistance sections2Ia, 22a, and 25a,,1c1ose s its contacts 260 in the series- .parallelresonantjrelay circuit 30b, and closes its contacts 26d n-theseries-parallel resonant relay circuit 49b. Closure of the'contacts 26cand 26d has no efiect, at-this time since the contacts I5d and 461) areopen. By short circuiting the resistance sections 2m, 22a, and 23a, theoperation of the contactor 26 to its energized position increases thehoisting torque of the motor I0.

When the frequency of the secondary voltage decreases to a valuecorresponding to approxi- -mately 40% of the synchronous speed of the 1motor III, the impedance of the series resonant circuit'SIIa has soincreased that the energization of the winding 3 Iw has decreasedsufficiently to permit the contacts 3Ia and 3Ib to reclose. Closure ofthe contacts 3| a has no operative effect at this time.

If the master switch 60 is now moved to the third position in thehoisting zone, or if it is already in that position, an energizingcircuit for the winding 21w is completed from the segment II through aconductor H2, the contacts 3Ib and 460, and the winding 2120 to theconductor [4. As a result of the energization of its operating winding21w, the contactor 2I closes its contacts 21a and 21b to short circuitthe additional resistance sections 2Ib, 22b, and 23b and closes itscontacts 210 to partially complete an energizing circuit for the winding28w of the contactor 28. Short circuiting of the resistance sections2"), 22b, and 23b causes a further increase in the torque of the motorI0.

Acceleration of the motor I to a speed equal to approximately 70% of itssynchronous speed causes a decrease in the energization of the winding4Iw of the relay M as a result of an increase in the impedance of theseries resonant circuit 40a due to the reduction in the frequency andmagnitude of the secondary voltage. The decrease in the energization ofthe winding 4I'w permits the contacts Ma and 4Ib to reclose. Closure ofthe contacts 4Ia has no operative effect at this time.

If the master switch 60 is now moved to the fourth position in thehoisting zone, or if it is already in the fourth position, an energizingcircuit for the winding 28w is completed from the contact segment I5,through a conductor 9|, the contacts Nb and 210, and the winding 28w tothe conductor H4. As a result of the energize.- tion of its operatingwinding 2820, the contactor 28 closes its contacts 28a and 28b to shortcircuit the additional resistance sections 2 to, 220 and 230 and closesits contacts 280 to partially complete an energizing circuit for thewinding 2910. The hoisting torque of the motor IB is again increased.

When the speed of the motor ill reaches approximately 85% of synchronousspeed, the secondary voltage and frequency are such as to cause adecrease in the energization of the winding Iw of the relay 5| whichpermits the contacts 5 Ia to reclose.

If the master switch 60 is now moved to the fifth position in thehoisting zone, o if it is already in that position, an energizingcircuit for the winding 29w is completed from the contact segment 14through a conductor 92, the contacts Sid and 280, and the winding 29w tothe conductor I I4. As a result of the energization of its operatingwinding 29w, the contactor 29 closes its contacts 29a and 29b to shortcircuit the additional resistance sections Zld, 22d, and 23d. Thehoisting torque of the motor Iii is again increased. All of thesecondary resistance 20.15 now short circuited and the motor I0accelerates to its normal running speed, its actual speed depending uponthe size of the load being hoisted.

Returning the master switchBO to the 011" position causes reinsertion ofthe resistance sections d, c, b, and a in-the order named, andconsequent slow down and stoppage of the motor I0. At the "ofP position,the winding 48w of the relay 48 is de-energized and the contacts 48a and48b open to cause de-energization of the brake winding 41w andconsequent application of the brake 4! which assists in bringing theload to a standstill and holds it in its hoisted position.

If the master'switch 60 is moved from the "oil position to the firstposition in the lowering zone, the brake 41 is released as hereinbeforedescribed and the operating windings I 6w, I8w and 26w are energized insuccession in the order named. The energizing circuit for the winding I8w is from the contact segment 63 through conductors 93 and I25, thecontacts 25d, the winding IBw, a conductor I26, and the contacts 380 tothe conducto H4. The energizing circuit for the winding I8w is from thecontact segment 65 through a conductor 94, the contacts "id and I5 andthe winding I820 to the conductor H4. The

energizing circuit for the winding 26w is from the conductor 94 throughthe contacts I611, a conductor 95, the contacts I80, the conductor H5,and the winding 2820 to the conductor H4.

The contactors I 6 and I8 operate in response to the energization oftheir operating windings IBw and I8w to close their contacts I6a, I6b,I8a, and I8b which connect the primary winding II for single phasebraking. The terminals I and 8 of the primary winding II areinterconnected by the contacts Ma and i8b and a point on theinterconnection is connected to the conductor L2 through the conductor39 and the contacts Hid. The terminal 9 of the primary winding H isconnected to the conductor L3 through the contacts IBb. Operation of thecontactor IE to its energized position also closes the contacts I60which complete a holding circuit for the winding I 6w which becomeseffective when the master switch 60 is returned to the ofi position ashereinafterdescribed, closes the contacts I6d in the circuit of thewindings i810 and 2620, and opens its contacts Ifie and IS in energizingcircuits for the windings 28w and 23w, respectively. Operation of thecontactor I d to its energized position also closes its contacts We inthe circuit of the winding 2820 and opens the contacts I36 and ltd whichserve as interlocks with the contactor 2G and thecontactors i5 and I 1,respectively.

The contactor 25 operates in response to energization of its operatingwinding 2620 to close its contacts 2% and 2621 which short circuit theresistance sections Zia, 22a, and 23a. The secondary circuit of themotor now includes a predetermined amount of the resistance 20. Theoperation of the contactor 26 to its energized Position also causesclosure of the contacts 260 and 2812 in the relay circuits 30 and 40,respectively, completing the series-parallel resonant circuits 3% and4%, respectively. The conditions of operation of the relays 3i and M areof no consequence while the master switch is in the first loweringposition and the effect of the series-parallel connection is describedin detail hereinafter in connection with the return of the master switch60 to the "01? position.

A portion of the primary winding II is now short circuited and a portionis energized by a single phase current from the conductors L2 and Withthe resistancesections b, c, and at now in the secondary circuit, thebraking torque of the motor II] is a maximum for all speeds both aboveand below s'ynchronism. This type of braking connection is claimed andmore fully described in Wilcox Patent No. 2,233,501, issued March 4,1941. While the single phase braking connections are completed, nodownward motor torque is produced so that small loads are not forceddownward, and, if an overhauling load is on the hoist, the motor exertsa braking torque.

A small amount of downward motor torque is obtained upon movement of themaster switch 60 to the second position in the lowering zone.

. The windings 18w and 2620 are de-energized upon movement of the masterswitch 60 to the second lowering position by interruption of the circuitbetween the contact segment 65 and the conductor 94 and the contactorsI8 and 26 return to their de-energized positions. Opening of thecontacts lila and I8!) removes the short circuit from the primarywinding i l and opening of the contacts 26a and 26b removes the shortcircuit from the resistance sections Zla, 22a, and 23a. The winding lfiwis maintained energized and the windings I510, 46w and 69w are energizedto cause operation of the contactor l and the relays 46 and 49,respectively. The energizing circuit for the winding 49w is from thesegment 62 through a conductor I30, the winding 49w, and a conductor l3lto the conductor I26. The energizingcircuit for the Winding i511) isfrom the conductor 88 through a conductor M8, the contacts 49a, theconductor 89, the winding l5w, the conductors 99 and 98, and thecontacts l8d to the conductor H4. The energizing circuit for the winding5620 is from the conductor 89 through the contacts I 5e and the winding$610 to the conductor Ht. Energization of the winding l5w causes thecontactor l5 to close its contacts 151: and i512 so that the primarywinding H is now connected to the conductor Ll through the contacts l5a,to the conductor L2 through the contacts l5b and Mia, and to theconductor L3, through the contacts I6b, thus causing the motor ill toexert a downward torque.

The contacts 260 and 26d also open in the second lowering position tointerrupt the seriesparallel resonant circuits 30b and 40b,respectively. Operation of the contactor l5 to its energized positionalso causes the opening of its contacts H511 to interrupt theseries-parallel resonant circuit 30b, closure of its contacts l5c whichcomplete the series resonant circuit 30a, closure of its contacts l5e,and opening of its contacts 15) in the circuit of the winding i811).Operation of the relay @9 to its energized position causes closure ofthe contacts 59a in the circuit of the winding Hill as just describedand also causes closure of the contacts ash and Q90 in the circuits ofthe windings 28w and 29w, respectively. Operation of the relay $6 inresponse to the energization of its winding @610 causes closure of thecontacts eta to complete the series resonant circuit 60a, opening of itscontacts 661) to interrupt the series-parallel resonant circuit 02), andclosure of its contacts #300 to partially complete a circuit to thewinding 21w. If the motor as is at standstill or rotating at a speedless than 40% of synchronism, the relay windings 35w, the, and 5Iw areeach energized by the secondary voltage drop as during hoistingoperations and the contacts 3m, 3ib, lla, Mb, and 5 la are open.

With the master switch 60 in the second lowering position, accelerationof the motor l0 to 40% of its synchronous speed causes reducedenergization of the winding Siw oi the relay 3! and consequent reclosureof the contacts 3Ia and 3ib. Closure of the contacts 3Ia has no eiiectat this time, but closure of the contacts 3|b results in energization ofthe operating winding Elw and consequent operation of the contactor 21.The energizing circuit for the winding 2lw is from the segment 6%through the conductor H2, the contacts 3lb and 460, and the winding 21wto the conductor I4. Operation of the contactor 21 to its energizedposition causes closure of its contacts 21a and 21b to short circuit theresistance sections a and b in each of the three branches of theresistance 20.

Closure of the contacts 210 due to energization of the winding 21wpartially completes an energizing circuit for the operating winding 28wof the contactor 28. When the speed of the motor 10 increases to of itssynchronous speed, the winding lw is practically de-energized and thecontacts Ma and Mb reclose. Closure of the contacts Ala has no efiect atthis time, but closure of the contacts llb completes an energizingcircuit for the winding 28w over a circuit from the conductor 88 throughthe contacts 49b, Mb, and 210 and the winding 28w to the conductor H4.The contactor 28 in response to the energization of its winding 28wcloses its contacts 28a and 28b to short circuit all of the resistancesections except sections Zld, 22d, and 23d causing the lowering torqueof the motor to increase. The contacts 280 also close and partiallycomplete a circuit to the winding 29w.

When the motor ID has accelerated to approximately of its synchronousspeed, the energization of the winding 5|w is reduced and the contacts5la close to complete an energizing circuit for the winding 29w from theconductor 88 through the contacts 69c, 51c, and 280 and the winding 29wto the conductor Hi. The contactor 29 in response to the energization ofits winding 29w closes its contacts 29a and 29b to short circuit theremainder of the resistance 20. The motor Ill now operates at speedsslightly below synchronous speed if the load is not overhauling and atspeeds slightly above synchronous speed if the load is overhauling.

Movement of the master switch 60 to the third position in the loweringzone completes a circuit from the segment 56 through the conductor 90,the contacts 25e and We, the conductor H5, and the winding 26w to theconductor Hi. If the motor 50 has accelerated so that the contacts Bibof the relay 3! are closed, the closure of the contactor 26 has noefiect upon motor operation. If the motor has not had an opportunity toaccelerate to 40% speed, however, closure of the contacts 26a and 26b ofthe contactor 26 short circuits resistance sections Zia, 22a, and 23a.of the resistor 20 to increase the torque of the motor in.

When the master switch is moved from the first lowering position to thesecond lowering position, all of the resistance 20 is in the secondarycircuit until approximately 40% speed is reached. The motor thus exertsat first a small downward torque. If the master switch is moved quicklyfrom the ofi position to the third or subsequent lowering positions ahigher lowering torque is immediately available due to the fact that thecontacts 26a and 25b close without time delay. The relays 3i, M and 5!are responsive in the third and subsequent lowering positions in thesame manner as in the second position lowering to effect sequentialenergization of the windings 2710, 2810, and 20w and consequentoperation of the contactors 21, 28, and 29 to their energized positions.Movement of the master switch 60 from the third to the fourth or fifthpositions in the lowering zone does not effect further change in themotor connections during power or regenerative lowering.

Movement of the master switch 60 back to the "off position from anyposition in the lowering zone causes the motor torque to be discontinuedand the brake 41 to be applied. When the master switch moves from thesecond position through the first lowering position, it is obvious thatthe operating winding I6w remains energized and that the operatingwindings 18w and 2610 are again energized as described hereinbefore toset up single phase braking connections and cause retardation of themotor III. Movement from the first lowering position to the "offposition does not efiect de-energization of the windings IIiw, I8w, and2620 at once. The contactor I6 remains in its energized position byvirtue of an energizing circuit for its winding I610 from the segment 64through the conductor II2, the contacts 3Ia, Ma, and I 60, the conductorI25, the contacts 25d, and the winding I6w to the conductor I26. Thecontactor I8 remains in its energized position by virtue of anenergizing circuit for its winding I 811; from the segment 65, throughthe conductor 94, the contacts "id and I5f, and the winding I8w to theconductor H4. The contactor 26 remains in its energized position byvirtue of an energizing circuit for its winding 26w from the conductor94 through the contacts I6d, the conductor 95, the contacts I80, theconductor H5, and the winding 26w to the conductor II4.

The contacts I50 and 4611 open, and the con tacts 26c, 2611, I501, and46?) close upon energization of the winding 26w and de-energization ofthe windings I5w and 46w as the master switch 60 moves from the secondlowering position to the off position, and consequently the seriesresonant circuits 30a and 40a are interrupted and the series-parallelresonant circuits 30b and 40b are completed. It is to be noted thatsince the winding 2610 is not energized until the contactor I8 is in itsenergized position, all transients in the secondary circuit havesubsided before the contacts 260 and 26d close.

During single phase braking there are two distinct currents in eachbranch of the secondary circuit of the motor Iii. Assuming a 60 cyclesource of supply, one of these currents is a positive sequence currentthat varies in frequency from zero cycles per second at synchronousspeed in one direction of rotation to 60 cycles per second at standstilland to 120 cycles per second at synchronous speed in the oppositedirection of rotation. The other current is a negative sequence currentthat varies from 120 cycles per second at synchronous speed in thedirection causing the positive sequence current to be at zero frequencyto 60 cycles per second at standstill and to zero cycles per second atsynchronous speed in the opposite direction of rotation, that is, atsynchronous speeds, one of the two sequence currents has a frequency of120 cycles per second, whereas the other one has a frequency of zerocycles per second and at zero speed the frequency of the currents isequal and is 60 cycles per second.

The series-parallel resonant circuits 3% and 40b are set to causeoperative energization of the windings 3Iw and 4Iw when the frequency ofthe voltage across the voltage dividers 32 and 42 approaches thefrequency of the source, or 60 cycles per second if a 60 cycle source isassumed. As the motor approaches zero speed, both the positive sequencecurrents and the negative sequence current are approaching 60 cycles persecond, and therefore both currents affect the relay circuits 30b and40b in a similar manner.

The windings 3Iw and 4Iw remain de-energized during single phase brakingas long as the motor I0 is rotating above a predetermined minimum speed.The frequency-current curves of the series-parallel resonant circuits 3%and 401) are peaked at 60 cycles and are at a low current value at allfrequencies substantially above and below 60 cycles per second. As the.motor I0 is decelerated due to single phase braking torque, the currentthrough one or the other or both of the windings 3Iw and H10 increasesrapidly at a predetermined value of motor speed close to zero speed andcauses operation of either or both of the relays 3I and 4| to theirenergized positions. The contacts 3Ia or 4I a, or both, thereupon opento interrupt the circuit to the operating winding I6w of the contactorI6. De-energization of the winding I6w causes the contactor I6 to openits contacts I6d which interrupts the circuits to the windings I82 and2620 and the contactors I8 and 26 thereupon open their contacts I8a andI8b and 26a and 261) which together with the opening of the contacts I6aand I6!) removes the single phase braking connections. The motor In isnow rotating at a slow enough speed to permit the holding brake 41 tobring it to standstill. When the master switch 60 is moved to the oil?position from the lowering positions, both single phase braking andfriction braking are in eiiect since the relay 48 is de-energized andthe contacts 480. and 48b are open to cause de-energization of theoperating winding 4lwof the brake 41 as soon as the off position isreached. The motor I0 is thus quickly brought to a standstill and thesingle phase connections are automatically removed to prevent acontinuous flow of current through the short circuited portion of theprimary winding II.

It is to be noted that the relay circuit 36 is connected forenergization from the branch 2i of the secondary resistor 20 whereas therelay circuit 40 is connected for energization from the branch 23. Thisis because at or near standstill, when the operation of the relays 3|and 4| is to be effected, the secondary current is unevenly distributedamong the three branches of the secondary circuit. In one position ofthe secondary winding H! with respect to the primary winding II, thecurrent in two of the branches might be at a maximum value while thecurrent in the third branch might be at a minimum value which is closeto zero. In another position of the secondary with respect to theprimary, might be approximately 85% of their normal value and thecurrent in the third branch onehalf of its normal value. However, one ofthe branches 2| or 23, at all times during single phase braking, has acurrent in excess of onehalf of the normal value although the other ofthe branches 2| or 23 might at the same time have a current value ofnearly zero. By using both relay circuits 30b and 40b during singlephase braking and connecting the contacts 3Ia and Me in series with thewinding I6w, it is always possible to have a sufficient voltage dropacross either branch 2i or 23'for one or the other of the windings 3Iwand M2 to be energized to effect operation of the contactor I6 to itsde-energized position. i

If it is desired to lower a load by countertorque control, the pushbutton 31 may be closed and the master switch 60 moved to or remain inany one of the positions in the lowering zone.

the currents in two of the branches With the push button 31 closed andthe master switch 60 in the lowering zone, a circuit is completed fromthe contact segment 63 through the conductors 93 and I32, the pushbutton 31, the operating winding 39w of the relay 39, and a conductorI36 to' the conductor M. The relay 35 in response to the energization ofits winding 39w closes its contacts 39a and opens its contacts 39b.Opening of the contacts 3% disconnects the conductor H4 fromtheconductor M, and closure of the contacts 390. completes a circuit fromthe conductor I32 through the conducto'r I31 and the operating winding38w of the relay 38 to the conductor M. The relay 38 in response to theenergization of its winding 38w closes its contacts 38a, 38b and 38e andopens its contacts 380 and 38d. While the push button 31 is held closed,the contacts 380 and 38b are both open and all of the directional,dynamic braking, and accelerating contactors are deenergized and thebrake contactor 48 is de-energized to cause application of the brake 31.Consequently closure of the push button 31 while the master switch 60 isin the lowering zone causes complete de-energization of the motor l andapplication of the brake 61 to cause the load to remain at standstill.

Opening of the contacts 38d interrupts the circuit through the operatingwinding 2510 of the contactor 25. De-energlzation of the winding 25wcauses opening of the contacts 25a, 25b, 25c, 25d and 25e. Opening ofthe contacts 25a, 25b and 250 removes the short circuit from theresistance section 2lr, 221' and 231', opening of the contacts 25dinterrupts all possible energizing circuits for the winding lfiw of thecontactor l6, and opening of the contacts 256 prevents energization ofthe winding 25w from the segment 66. Closure of the contacts 38bpartially completes a circuit to the winding 1110 and closure of thecontacts 38c partially completes a circuit to the winding 21w.

Closure of the contacts 380 completes a holding circuit for the winding38w from the conductor 132 to the conductor I31 which is independent ofthe contacts 39a. Re-opening of the push button 31 consequentlyde-energizes the winding 3910 but does not de-energize the winding 38w.Reclosure of the contacts 33b as a result of the de-energization of thewinding 39w reconnects the conductor lid to the conductor l4 and causesenergization of some or all of the accelerating contactors dependingupon the position of the master switch 63 in the lowering zone. However,since the contacts 38cjremain open after re-opening of the push button31, the relay 49 and the contactor it cannot be energized. Closure ofthe contacts 39b while the contacts 38b are closed causes energizationof the winding I'lw of the contactor 11 over a circuit from theconductor 88 through the conductor 1 18, the contacts 38b, theconductors 91 and 96, the winding 11w, the conductor 93, and thecontacts 1802 to the conductor H4. Closure of the contacts l'lc as aresult of the energization of the winding llw completes an energizingcircuit for the winding 15w of the contactor l5 by interconnecting theconductors 91 and 83. Closure of the contacts We as a result of theenergizationof the winding w completes an energizing circuit for thewinding 4621; of the relay 46 by interconnecting the conductor 39 andthe winding 46w.

Closure of the contacts 11a, 11b, 15a. and l5b connects the primarywinding H of the motor E0 to the source of power so that it exerts ahoisting torque. The hoisting torque is greatly reduced however fromthat available when the master switch is in the hoisting positions dueto the fact that the resistance sections Zlr, 221- and 231' are nolonger short circuited, but are efiective in the secondary resistor 20.Thus the closing and opening of the push button 31 while the masterswitch is in the lowering zone renders the lowering zone acounter-torque zone.

It is thus seen that if the push button 31 is closed at any time whilethe master switch 63 is in any of the positions in the lowering zone,

the motor I0 is disconnected from the source of supply and the brake 41is applied. If the pushbutton 31 is re-opened while the master switch 60remains in any of the lowering positions, the motor I0 is connected tothe source of supply so as to exert a hoisting torque and the brake 41is released. The push button 31 may be closed and opened quickly so thatthe transfer from lowering connections to hoisting connections occursbefore the brake 41 has time to operate. After the push button 31 hasbeen closed and opened while the master switch 60 is in any of thelowering positions, the master switch 60 may be moved to any other ofthe lowering positions to obtain speed control in the lowering ofoverhauling loads. The farther that the master switch 60 is moved fromthe ofi position the less the counter-torque and the greater thelowering speeds.

When the master switch 60 is in the first lowering position and the pushbutton 31 has been closed and opened the contactors 21, 28 and 29 are intheir energized positions and all of the resistor 20 is short-circuitedexcept the section 231'. The secondary circuit is therefore unbalancedand the motor Ill exerts a hoisting torque which permits overhaulingloads to be lowered at a slow speed. The circuit to the winding 21w isfrom the conductor H2 through the contacts 38:; and 330. The circuit tothe winding 2810 is from the segment 63 through a conductor I40 and thecontacts [6e and 210. The circuit to the winding 29w is from the segment68 through a conductor EM and the contacts ltf and 280.

The counter-torque is decreased and the lowering speed increased uponmovement of the master switch 60 from the first to the second loweringposition due to de-energization of the winding 2910 by interruption ofthe circuit between the segment 68 and the conductor Ml. De-energizationof the winding 29w permits the contacts 29a and 23b to open, removingthe short circuit from the resistor sections 21d, 22d, and 23d. Theresistor 26 remains unbalanced due to the inclusion of the section 231'in the branch 23.

A further decrease in counter-torque and consequent increase in thelowering speed of overhauling loads is obtained upon movement of themaster switch 60 from the second to the third lowering postlon. In thethird lowering position, the energizing circuit for he winding 28w isinterrupted between the segment 69 and the conductor i 30 and thecontacts 28a and 281) open to remove the short circuit from the sectionsZlc, 22c, 23c and 221'. The resistor 20 remains unbalanced because ofthe inclusion of the sections 22? and 231' in the branches 22 and 23,re-

spectively.

When the master switch moves from the sec- 0nd to the third loweringposition the winding 2610 is energized over a circuit from the segment67, a conductor M2, the contacts 17d and the conductor H5. The contactor28 in response to the energization of its winding 26w closes itscontacts 26a and 26b to short circuit the sections Zia, 22a and 23a.While the master switch '60 is in the third position closure of thecontactor 26 has no operating eflect since the contacts 21a and 21b areclosed. r

In the fourth lowering positionthe circuit to the winding 21w isinterrupted between the segment 64 and the conductor 2 which permits thecontacts 21a, and 21b to open, removing the short circuit from theresistor sections 2), 22b, 23b, and 2lr. The resistor 20 is now balancedbut since the r sections are included with the d, c, and 12 sections,the motor l does not exert an extremely high hoisting torque, but atorque sufficient to permit heavy overhauling loads to be lowered quiterapidly.

Upon movement of the master switch 6d from the fourth to fifth loweringposition, the circuit to the winding 2810 is interrupted between thesegment El! and the conductor Hi2 so that the contacts 260; and 26b opento insert all of the resistor Ed into the secondary circuit of the motorit], The counter-torque of the motor it under these conditions isextremely weak and overhauling loads are lowered at a rapid rate.

The relay circuit tilt is adjusted so that the winding ifilw becomesenergized sufficiently to close the contacts l2la when the frequency ofthe current in the secondary winding ill, assuming a 60 cycle source, isapproximately 130 cycles. secondary frequency of 130 cycles is obtainedwhen an overhauling load is driving the motor ill at approximately 115%of synchronous speed in the opposite direction from that of the rotationof the magnetic field set up by the primary winding ll. Closure of thecontacts iilla cornpletes an energizing circuit to the winding 28m fromthe conductor it, thus when the master switch is in the fourth or fifthlowering position and the motor speed, due to counter-torque low ering,exceeds 115% of synchronous speed, the contactor it closes the contactstho and iliib to short circuit the a, b, and 0 sections and the sectionsQir and 22?" of the resistor 2d, which slows down the motor ill andcauses it to run at the speed it would have it the master switch 60 werein the second lowering position.

During counter-torque lowering the frequency of the secondary current orthe motor it is above that of the source and consequently the relays 3l, ii, id, and 55 remain in their deenergized posi tions.

We claim:

1. In a braking control system for a wound rotor induction hoist motor,the combination comprising a hoist motor, a movable controller, saidcontroller being provided with an ofi" position, a zone forsingle-=phase braking contiguous to said ofi position, a zone forgraduated degrees of sition, and means operable in cooperation with saidcontroller to connect said motor for exerting a hoisting torque lessthan said weakest hoisting torque when the controller is in other thanthe OE position and hoisting zone.

2. In a braking control system for a wound to said 0 position and asub-zone for graduated degrees of power lowering contiguous to saidsingle phase braking sub-zone with the position nearest the single phasebraking sub-zone permitting the least rapid power lowering accelerationof the motor, a manual switch means operative only while said controlleris in said lowering zone, and means responsive to operation of saidmanual switch means to render said lowering zone operative as acounter-torque zone with the position of greatest counter-torque nearestsaid ofi position.

3. The combination with a control system for a polyphase wound rotorinduction motor subject to overhauling loads and having a primarywinding and a secondary winding and comprising a polyphase resistancenetwork adapted to be connected to said secondary winding to form, whenso connected, a closed polyphase network with said secondary winding,forward means operable to connect said primary winding to a source ofpolyphase power for causing said motor to exert a torque assisting thetorque of the overhauling load, reverse means operable to connect saidpri mary winding to a source of polyphase power for causing said motorto exert a torque opposing the torque of the overhauling load, brakingmeans operable to connect a portion of said primary winding to a sourceof single phase power and to short circuit a portion of said primarywinding, a multi-position master switch movable to different positionsfor causing operation of said forward means, reverse means, and brakingmeans, respectively, of means operable, while said master switch is inthe position normally causing operation of said forward means, to causeoperation of said reverse means instead of operation or? said forwardmeans.

i. In a braking control system for a wound rotor induction motor, amovable controller including a plurality of switching devices, saidcontroller being provided with an oil position, a single phase brakingzone contiguous to said off position, and a power lowering zonecontiguous to said single phase braking zone, some of said switchingdevices being operable when the controller is in said single phasebraking zone to connect said motor for single phase braking, some ofsaid switching devices being operable when the controller is in saidpower lowering zone to connect said motor for power lowering with theacceleration due to power lowering being least when said controller ismoved to a position in said power lowering zone closest to said singlephase braking zone, means operable while said controller is in saidpower lowering zone to render some of said switching devices inoperativeand other of said switching devices operative to render said singlephase braking zone and said power lowering zone a zone of counter-torquebraking, said operation of said switching devices causing thecountertorque to be greatest when said controller is moved closest tosaid oil position.

5. In a braking control system for a wound rotor induction hoistingmotor, a movable controller including a plurality of switching devices,said controller being provided with an off position and a powerloweringzone, some of said switching devices being operative when saidcontroller is in the power lowering zone to connect said motor for powerlowering, a manual means having two positions of movement, meansresponsive to movement of said manual means to one of said positions torender some of said switching devices operative to de-energize saidmotor, means responsive to movement of said manual means to the other ofsaid positions to render some of said switching devices operative toconnect said motor for hoisting, and means operable to render saidswitching devices operative in response to movement of said manual meansonly while said controller is in said power lowering zone.

6. A motor control system for hoists and the like subject to overhaulingdescending loads and driven by a polyphase wound rotor induction motor,a balanced secondary resistance adapted to be connected in a closednetwork with the secondary winding of said motor, means for controllingthe direction and speed of said motor comprising a plurality ofcontactors and a master switch, said master switch having an oilposition, a hoisting position, and a plurality of lowering positions, acontact segment means on said master switch operable in the loweringpositions for completing a circuit for energizing some of saidcontactors to'connect the motor to a source I of power for exerting atorque assisting the torque of the overhauling load, said contactsegment means including means for concurrently partially completinganother circuit, a manual switch means in said partially completedcircuit operable to complete said circuit for causing some of saidcontactors to unbalance said secondary resistance and reverse said motorconnections.

'I. The combination with a control system for a polyphase wound rotorinduction motor subject to overhauling loads and having a primarywinding and a secondary winding and comprising a polyphase resistancenetwork adapted to be connected to said secondary winding to form, whenso connected, a closed polyphase network with said secondary winding,resistance adjusting means operable to balance and unbalance said closednetwork selectively, a master switch having a forward position and areverse position, means operative while said master switch is in saidforward position to connect said primary winding to a source of powerfor causing said motor to exert a torque assisting the torque of theoverhauling load, and means operative while said master switch is insaid reverse position to connect said primary winding to said source ofpower for causing said motor to exert a torque opposing the torque ofthe overhauling load, a control circuit, of manual means operable toaffect the conductivity of said circuit to render said circuitoperative, only when said master switch is in said forward position, tosubstantially concurrently reverse the connections between said primarywinding'and said source and to cause said resistance adjusting means tounbalance said network.

8. A combination in accordance with claim 7 characterized in that saidmanual means has two operative positions of movement and that means areprovided responsive to movement of said manual means to one of saidpositions to affect the conductivity of said circuit to cause therebyde-energizationof said motor.

9. A combination in accordance with claim '7 characterized in that saidcircuit is responsive 7 to the manual means for de-energizing said motorand that said manual means has two positions of movement, one of whichsaid positions causes the circuit to efiect said reversal of theconnection between said primary winding and the source, the other ofwhich positions causes said circuit to efiect said de-energization ofthe motor, and one of said two positions causes said circuit to efiectsaid unbalance.

10. The combination with a control system for a polyphase wound rotorinduction motor subject to overhauling loads and having a primarywinding and a secondary winding and comprising a polyphase resistancenetwork adapted to be connected to said secondary winding to form, whenso connected, a closed polyphase network with said secondary winding,resistance adjusting means operable to balance and unbalance said closednetwork selectively, a master switch having a neutral position and aplurality of running positions, means operative while said master switchis in said running positions to connect said primary winding to a sourceof power for causing said motor to exert a torque assisting the torqueof the overhauling load, reversing means to reverse the connectionbetween said primary winding and the source, circuit control meansincluding contact segments on said master switch operable as said masterswitch is moved further from said neutral position through said runningpositions to increase said assisting torque, of manual means operablefor causing, only when said master switch is in said running positions,substantially concurrently unbalance of said closed network by saidresistance adjusting means and reversal of the motor torque by saidreversing means, and additional segments on said master switch renderedoperable upon operation of said manual means to cause said circuitcontrol means to decrease the reverse torque of the motor as said masterswitch is moved further from said neutral position through said runningpositions.

11. In a control system for hoisting mechanism, the combination with aninduction motor comprising a stator and a rotor subject to anoverhauling load, a resistor for varying the torque of said motor, acontroller comprising switches at a series of stations for establishingcircuits for controlling the direction and magnitude of the torque ofsaid motor, hoisting switching means responsive to the controller at afirst station for connecting the stator of the motor to a polyphasesource of power so that the motor exerts a hoisting torque tending toraise the load, resistance adjusting means responsive to the controllerfor adjusting said resistor to vary said hoisting torque throughout amaximum range, braking switching means responsive to the controller at asecond station for short-circuiting a portion of the stator andconnecting a portion of the stator to a single phase source of power,and lowering switching means responsive to the controller at a thirdstation for connecting the stator to a polyphase source of power so thatthe motor exerts a torque tending to lower the load, of manual meansassociated with said controller and operable for causing said resistanceadjusting means to adjust said resistor when said controller is at saidthird station, and means operable in response to operational said manualmeans for preventing operation of said lowering switching means andcausing operation of said hoisting switching means so that'the motorexerts a hoisting torque, adjustment of said resistor by operation ofsaid manual means causing said hoisting torque to be variable throughouta minimum range.

BRUCE E. McARTI-IUR. ASA H. MYLES.

